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 Post subject: I’m rich! Not in the good way though...
PostPosted: Sat Nov 11, 2017 4:47 am 
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Joined: Nov 11, 2017
Motorcycle: 1999 CMX250c
Rebel: 250
Country: US
State/Province: FL
City: Daytona
I recently bought a 99 250 for my wife, and as soon as I rode it I smelled gas. The guy I got it from said he had just rebuilt the carburetor, so I thought great, maybe the float was just stuck..nothing a few light taps with a hammer wouldn’t fix, used to do it on my dirt bike. Didn’t help, so I opened up the carb, but before opening hehe, I noticed it was a 450 carb on a 250 bike. Turns out that none of the jets were cleaned, and the float was broken where the float pin hangs...rebuilt my a$$. I ordered a new float, pin, and cleaned the jets in hopes that I could just adjust the 450 carb to work with the 250, but no matter what, this thing is running rich as hell. My question is, can I get smaller jets for this thing, small enough for a 250, or is the only solution to buy a new carb?


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 Post subject: Re: I’m rich! Not in the good way though...
PostPosted: Sat Nov 11, 2017 7:09 am 
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Joined: Feb 23, 2009
Motorcycle: Rebel 250 plus a few others
Rebel: 250
Country: Canada
State/Province: NB
City: Fredericton
cmx450 twin carbs are 29.5 mm throat diameter vs 26 mm for the 250. That is an increase of 28% in throat area. Given that the 450 carbs each feed one cylinder every 2 revolutions versus the single 250 feeding one smaller cylinder each revolution, the peak design flow through the 450 carb would be twice as much as for the 250, but the total flows would be similar. In theory I should think the 450 carb would be within range of the proper mixture for the 250, provided suitable jets could be found and dialled in by trial and error. I would also think that getting a 250 carb would be much easier unless someone else has already done this and can provide the information you need.

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 Post subject: Re: I’m rich! Not in the good way though...
PostPosted: Sun Dec 03, 2017 12:35 am 
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Joined: Jul 4, 2009
Motorcycle: 2016 Honda Rebel
Rebel: 250
Country: USA
State/Province: AZ
City: Chandler
I would definitely look for a proper 250 carb. Carbs are finicky (but dead reliable when clean and properly jetted) and it will likely never run quite right with a 450 carb on it, no matter what you do to it. I'm surprised that a 450 carb would even fit. Does it have a stock airbox? Has the intake manifold been modified in some way? Given the 3.5mm difference in diameter, I suspect the 450 carb would flow too much air for the 250. It might work well at full throttle, but probably not at slower speeds.

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